Thin-film common mode filter and thin-film common mode filter array

ABSTRACT

A thin-film common mode filter is provided, comprising: a pair of magnetic plates; upper/lower coil conductors formed between the magnetic plates, spirally wound in the magnetic plate surface direction, overlapped each other; upper/lower lead conductors one ends of which are connected electrically to one ends in centers of the upper/lower coil conductors, respectively, extended to external portions across these coil conductors; an upper/lower lead drawing terminals to which the other ends of the upper/lower lead conductors are connected, respectively; an upper/lower coil drawing terminals to which the other ends of the upper/lower coil conductors are connected, respectively; and each of the lower lead/coil drawing terminals and the upper coil/lead drawing terminals having a structure where at least two of conductor layers to be patterned into the upper/lower lead conductors and the upper/lower coil conductors are stacked, and brought into conduction with each other.

PRIORITY CLAIM

This application claims priority from Japanese patent application No.2003-398964, filed on Nov. 28, 2003, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin-film common mode filter and athin-film common mode filter array.

2. Description of the Related Art

Common mode filter is a device for suppressing common mode currents thatcause electromagnetic interference in parallel transmission lines. Thecommon mode filter has magnetically coupled inductors to remove in-phasenoise component.

Thin-film common mode filter miniaturized and highly integrated byforming bilayered thin-film coils between ferrite substrates and byconstructing in chip form, and thin film common mode filter array onwhich a plurality of the filters are mounted, are described in forexample, Japanese Patent Publications Nos. 04-364709A, 08-203737A,08-335517A and 11-054326A.

Generally, in such a thin-film common mode filter constructed in chipform, drawing terminals of outgoing parts from both ends of thethin-film coil are exposed on the side, and then external-connectelectrode terminals are formed on the chip side so that they can beconnected electrically to the exposed drawing terminals.

Conventional thin-film common mode filter, however, has small drawingterminals. Therefore, it has been a problem of reliability where, insome cases, the external-connect electrode terminal formed on the chipside has an incomplete electrical connection with the drawing terminal.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide athin-film common mode filter and a thin-film common mode filter arraypossessing an improved reliability in the electrical connection betweenthe drawing terminals and the external-connect electrode terminals.

According to the present invention, a thin-film common mode filter and athin-film common mode filter array comprised a plurality of thethin-film common mode filters are provided, the thin-film common modefilter comprising: a pair of magnetic plates; an upper coil conductorand a lower coil conductor formed between the pair of magnetic plates,spirally wound in the magnetic plate surface direction, and overlappedeach other; an upper lead conductor and a lower lead conductor, one endsof which are connected electrically to one ends in center portions ofthe upper coil conductor and the lower coil conductor, respectively, andextended to external portions across the upper coil conductor and thelower coil conductor; an upper lead drawing terminal and a lower leaddrawing terminal to which the other ends of the upper lead conductor andthe lower lead conductor are connected, respectively; an upper coildrawing terminal and a lower coil drawing terminal to which the otherends of the upper coil conductor and the lower coil conductor areconnected, respectively; and each of the lower lead drawing terminal,the lower coil drawing terminal, the upper coil drawing terminal and theupper lead drawing terminal having a structure where at least two ofconductor layers to be patterned into the lower lead conductor, thelower coil conductor, the upper coil conductor and the upper leadconductor are stacked, and brought into conduction with each other.

Each of the drawing terminal is formed by stacking a plurality of theconductor layers to be patterned into the lower lead conductor, thelower coil conductor, the upper coil conductor and the upper leadconductor and bringing the conductor layers into conduction with eachother. Therefore, because the side cross-sectional area of the drawingterminal, or the exposed area on the chip side, becomes larger, thedrawing terminals and the external-connect electrode terminals have amuch excellent electric connection between them, and a reliability inelectric connection is greatly improved.

Preferably, each of the drawing terminal has a structure where all ofthe conductor layers to be patterned into the lower lead conductor, thelower coil conductor, the upper coil conductor and the upper leadconductor are stacked, and brought into conduction with each other.

It is also preferable that each of the lower lead drawing terminal, thelower coil drawing terminal, the upper coil drawing terminal and theupper lead drawing terminal has a structure where the conductor layersto be patterned into the lower lead conductor and the lower coilconductor are connected to each other via a through hole in a firstlayer, the conductor layers to be patterned into the lower coilconductor and the upper coil conductor are connected to each other via athrough hole in a second layer, the conductor layers to be patternedinto the upper coil conductor and the upper lead conductor are connectedto each other via a through hole in a third layer, and all of theseconductor layers are brought into conduction with each other.

More preferably, in the case, centers of the through holes in the firstlayer to the third layer coincide with each other. Then, the throughholes in the first layer to the third layer may have the same form andthe same dimension as each other, further more preferably, the throughholes in the first layer to the third layer, that is, in the lower layerto the upper layer have sequentially larger dimensions. When the throughholes have the same dimension as each other, the drawing terminalportion has a large step, then some insulating material is likely toremain in the through holes under an influence of reflections duringexposure in photolithography, and therefore, a reliability in conductionis reduced (Especially, this problem becomes marked in the case of ahigh aspect-ratio pattern). However, by making the through holes in thelower layer to the upper layer sequentially larger, the step becomessmaller, and therefore, a reliability in the conduction between thelayers is improved.

It is also preferable that each center position of the through holes inthe first layer to the third layer is alternately changed. In the case,more preferably, the through holes in the first layer to the third layerhave the same form and the same dimension as each other. By alternatelychanging the position of each center of the through holes, the dimple ofthe conductor in the through hole becomes smaller, then the surface ofthe insulating layer thereon becomes flatter, and therefore, thesurfaces of the through hole conductors and of the insulating layersformed subsequently also become flatter. Consequently, a reliability inthe conduction between the layers is improved, and the step becomessmaller.

Preferably, widths (W₁) of said upper and lower lead conductors are lessthan twice the widths (W₂) of said upper and lower coil conductors(W₁<2W₂). The higher aspect ratios (height/width) of the coil patternand of the lead pattern cause smaller capacities between the coilconductors and between the coil conductor and the lead conductor. As theresults, the high-frequency transmission properties are improved.However, the higher aspect ratio design makes it difficult to narrow thespacing between the lead conductor and the coil conductor. To solve thedifficulty, narrowing the width of the lead conductor is effective.However, setting the width of the lead conductor (W₁) not less thantwice the width of the coil conductor (W₂) lowers the resonancefrequency to a large degree. Therefore, by setting W₁<2W₂, the thin-filmcommon mode filter showing less decrease in the resonance frequency canbe provided.

Preferably, the lower and upper lead conductors are formed of a copper(Cu) whose external surfaces are covered with nickel(Ni)/chromium(Cr)films. In the case, more preferably, a surface of the lower leadconductor in a connection portion between the lower coil conductor andthe lower lead conductor, and a surface of the upper lead conductor in aconnection portion between the upper coil conductor and the upper leadconductor, are covered with only chromium (Cr) films. A trouble of anelectric resistance increase caused by the diffusion between Cu/Ni canbe avoided because Ni is eliminated in the connection portion.

Further objects and advantages of the present invention will be apparentfrom the following description of the preferred embodiments of theinvention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an exploded perspective view schematically illustrating astructure of a thin-film common mode filter array according to anembodiment of the present invention;

FIG. 2 shows a perspective view schematically illustrating an appearanceof a thin-film common mode filter array when cut out of a wafer;

FIG. 3 shows another perspective view from the different direction fromthat in FIG. 2, schematically illustrating an appearance of a thin-filmcommon mode filter array when cut out of a wafer;

FIG. 4 shows a perspective view schematically illustrating an appearanceof the finished-up thin-film common mode filter array;

FIG. 5 shows an exploded perspective view schematically illustrating astructure of a thin-film common mode filter consisting of asingle-element in the thin-film common mode filter array in FIG. 1;

FIG. 6 shows a perspective view schematically illustrating an appearanceof the thin-film common mode filter when cut out of a wafer;

FIG. 7 shows a perspective view schematically illustrating an appearanceof the finished-up thin-film common mode filter;

FIGS. 8 a to 8 c show cross-sectional views of the thin-film common modefilter taken along line A—A, line B—B and line C—C in FIG. 5;

FIG. 9 shows a perspective view schematically illustrating structuresonly of the coil conductors, the lead conductors and the drawingterminals in the thin-film common mode filter according to theembodiment in FIGS. 1 and 5;

FIGS. 10 a to 10 c show cross-sectional views of a structure example ofthe drawing terminal;

FIG. 11 shows a magnified cross-sectional view illustrating a contactportion between the upper coil conductor and the upper lead conductor;

FIG. 12 shows a characteristic graph illustrating a relation between aresonance frequency of the thin-film common mode filter and a width ofthe lead conductor;

FIGS. 13 a to 13 j show perspective views for explanation of a waferprocess to produce the thin-film common mode filter array; and

FIGS. 14 a to 14 j show perspective views for explanation of a workingprocess to produce the thin-film common mode filter array.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exploded perspective view schematically illustrating astructure of a thin-film common mode filter array according to anembodiment of the present invention. FIG. 2 shows a perspective viewschematically illustrating an appearance of a thin-film common modefilter array when cut out of a wafer. FIG. 3 shows another perspectiveview from the different direction from that in FIG. 2, schematicallyillustrating an appearance of a thin-film common mode filter array whencut out of a wafer. FIG. 4 shows a perspective view schematicallyillustrating an appearance of a finished-up thin-film common mode filterarray.

The thin-film common mode filter array is formed as a chip by aligningtwo thin-film common mode filters.

In FIG. 1, reference numeral 10 indicates an insulating magneticsubstrate, 11 indicates a first insulating layer usually formed of apolyimide or a BCB (benzocyclobutene) that have great heat-resistance,stacked on the insulating magnetic substrate 10, 12 a and 12 b indicatea lower lead conductor formed on the first insulating layer 11, 13indicates a second insulating layer stacked thereon, 14 a and 14 bindicate a lower coil conductor with spiral form formed on the secondinsulating layer 13, 15 indicates a third insulating layer stackedthereon, 16 a and 16 b indicate an upper coil conductor with spiral formformed on the third insulating layer 15, 17 indicates a fourthinsulating layer stacked thereon, 19 indicates a fifth insulating layerstacked thereon, 20 indicates a insulating magnetic top-side board, 21 aand 21 b indicate an insulating magnetic material constituting a returnportion of a magnetic path in the center portion of the coil, and 22 aand 22 b indicate an insulating magnetic material constituting a returnportion of a magnetic path in the periphery of the coil, respectively.

As just described, the laminate 23 is sandwiched between the insulatingmagnetic substrate 10 and the insulating magnetic top-side board 20.

The lower coil conductors 14 a and 14 b spirally wound in the substratedirection, and the upper coil conductors 16 a and 16 b spirally wound inthe substrate direction, are positioned in mirror symmetry to each otherwith the third insulating layer 15 sandwiched between them.

The lower lead conductors 12 a and 12 b formed of the different layerfrom the layer patterned into the lower coil conductors 14 a and 14 blead conductive paths, via the second insulating layer 13, from one endsin center portions of these coil conductors into the outsides of theirspiral areas, respectively. Correspondingly, The upper lead conductors18 a and 18 b formed of the different layer from the layer patternedinto the upper coil conductors 16 a and 16 b lead conductive paths, viathe fourth insulating layer 17, from one ends in center portions ofthese coil conductors into the outsides of the spiral areas,respectively. In other words, one ends of the lead conductors 12 a, 12b, 18 a and 18 b are connected electrically, via through holes, to theends in center portions of the coil conductors 14 a, 14 b, 16 a and 16b, respectively, and then these ends constitute contact portions. Theother ends of the lead conductors 12 a, 12 b, 18 a and 18 b areconnected electrically to lead drawing terminals 24 a, 24 b, 25 a and 25b (FIG. 2) formed in the side edge portion of the thin-film common modefilter array, respectively. Correspondingly, the other ends of the coilconductors 14 a, 14 b, 16 a and 16 b are connected electrically to thecoil drawing terminals 26 a, 26 b, 27 a and 27 b (FIG. 3) formed in theside edge portion of the thin-film common mode filter array,respectively.

The insulating magnetic substrate 10 and the insulating magnetictop-side board 20 are usually formed of a NiZn ferrite. The first tofifth insulating layers 11, 13, 15, 17 and 19 are usually formed of apolylmide or a BCB (benzocyclobutene) that have great heat-resistance.

The lower lead conductors 12 a and 12 b, the lower coil conductors 14 aand 14 b, the upper coil conductors 16 a and 16 b and the upper leadconductors 18 a and 18 b are formed of Cu, the external surfaces ofwhich are covered with Ni/Cr films. However, the respective contactportions between the lower lead conductors 12 a and 12 b and the lowercoil conductors 14 a and 14 b, and the respective contact portionsbetween the upper coil conductors 16 a and 16 b and the upper leadconductors 18 a and 18 b, are covered with only Cr films.

In each of the thin-film common mode filter arrays, as shown in FIGS. 2and 3, the insulating magnetic substrate 10, the laminate 23 and theinsulating magnetic top-side board 20 are cut out, and then, as shown inFIG. 4, connect electrode terminals 28 a, 28 b, 29 a, 29 b, 30 a, 30 b,31 a and 31 b formed of such as a Ni alloy for being connectedelectrically to the drawing terminals exposed on the cut side-surfaces,are formed on the cut side-surfaces.

A single thin-film common mode filter may be included in the chip. FIG.5 shows an exploded perspective view schematically illustrating astructure of a thin-film common mode filter consisting of thesingle-element. FIG. 6 shows a perspective view schematicallyillustrating an appearance of the thin-film common mode filter when cutout of a wafer. FIG. 7 shows a perspective view schematicallyillustrating an appearance of the finished-up thin-film common modefilter. FIG. 8 shows a cross-sectional view of the thin-film common modefilter taken along line A—A, line B—B and line C—C in FIG. 5.

The structure of the thin-film common mode filter is the same as that ofthe thin-film common mode filter as one-half of the thin-film commonmode filter array shown in FIGS. 1 to 3. Therefore, in FIGS. 5 to 8, thesame elements as those in FIG. 1 have been referred to with samereference numerals.

FIG. 8 a shows a cross-sectional view taken along line A—A in FIG. 5,illustrating the center cross-section having no drawing terminals. Onthe cross-section, appear the lower coil conductor 14 a, the upper coilconductor 16 a, the insulating magnetic material 21 a constituting areturn portion of a magnetic path in the center portion of the coil, andthe insulating magnetic material 22 a constituting a return portion of amagnetic path in the periphery of the coil.

FIG. 8 b shows a cross-sectional view taken along line B—B in FIG. 5,illustrating the cross-section having the drawing terminals and theupper lead conductor. On the cross-section, appear the lower coilconductor 14 a, the upper coil conductor 16 a, the upper lead conductor18 a, the upper lead drawing terminal 25 a, the upper coil drawingterminal 27 a, and the insulating magnetic material 21 a constituting areturn portion of a magnetic path in the center portion of the coil.

FIG. 8 c shows a cross-sectional view taken along line C—C in FIG. 5,which illustrates the cross-section having the drawing terminals and thelower lead conductor. On the cross-section, appear the lower coilconductor 14 a, the upper coil conductor 16 a, the lower lead conductor12 a, the lower lead drawing terminal 24 a, the lower coil drawingterminal 26 a, and the insulating magnetic material 21 a constituting areturn portion of a magnetic path in the center portion of the coil.

Then, the structures of the lead drawing terminals 24 a, 24 b, 25 a and25 b, and of the coil drawing terminal 26 a, 26 b, 27 a and 27 b,according to the present embodiment will be described.

FIG. 9 shows a perspective view schematically illustrating structuresonly of the coil conductors, the lead conductors and the drawingterminals in the thin-film common mode filter according to the presentembodiment. FIG. 10 shows cross-sectional views of structure examples ofthe drawing terminal.

In FIG. 9, reference numeral 82 indicates a lower lead conductor, 84indicates a lower coil conductor, one end in the center portion of whichis connected to one end of the lower lead conductor 82, 86 indicates anupper coil conductor, 88 indicates an upper lead conductor, one end ofwhich is connected to one end in the center portion of the upper coilconductor 86, 94 indicates a lower lead drawing terminal connected tothe other end of the lower lead conductor 82, 95 indicates an upper leaddrawing terminal connected to the other end of the upper lead conductor88, 96 indicates a lower coil drawing terminal connected to the otherend in the outside of the lower coil conductor 84, and 97 indicates anupper coil drawing terminal connected to the other end in the outside ofthe upper coil conductor 86, respectively.

Each drawing terminal has a multilayered structure, not a monolayerstructure having only its own conductor layer, where all the otherconductor layers are stacked via through holes formed in the insulatinglayers interlayered between these conductor layers, and brought intoconduction with each other. In other words, the lower lead drawingterminal 94 has a structure where the conductor layers to be patternedinto the lower lead conductor 82, the lower coil conductor 84, the uppercoil conductor 86 and the upper lead conductor 88 are multilayered andbrought into conduction with each other. Therefore, because the sidecross-sectional area of the drawing terminal, or the exposed area on thechip side, becomes larger, the drawing terminals and theexternal-connect electrode terminals have a much excellent electricconnection between them, and a reliability in electric connection isgreatly improved.

As an embodiment of the multilayered structure of the conductor layers,as shown in FIG. 10 a, conductor layers 112, 114, 116 and 118 arepreferably connected to brought into conduction with each other viathrough holes 103 a, 105 a and 107 a formed in a second insulating layer103, a third insulating layer 105 and a fourth insulating layer 107,respectively, the through holes having an identical center, the sameform and the same dimension as each other.

Further, as shown in FIG. 10 b, conductor layers 112′, 114′, 116′ and118′ are preferably connected to brought into conduction with each othervia through holes 103 a′, 105 a′ and 107 a′ formed in a secondinsulating layer 103′, a third insulating layer 105′ and a fourthinsulating layer 107′, respectively, the through holes 103 a′, 105 a′and 107 a′ in the lower layer to the upper layer having an identicalcenter and sequentially larger dimensions. When the through holes havethe same dimension as each other like the structure in FIG. 10 a, thedrawing terminal portion has a large step, then some insulating materialis likely to remain in the through holes under an influence ofreflections during exposure in photolithography, and therefore, areliability in conduction is reduced. Especially, this problem becomesmarked in the case of a high aspect-ratio pattern. However, by makingthe through holes in the lower layer to the upper layer sequentiallylarger, the step becomes smaller, and therefore, a reliability in theconduction between the layers is improved.

Furthermore, as shown in FIG. 10 c, conductor layers 112″, 114″, 116″and 118″ are preferably connected to brought into conduction with eachother via through holes 103 a″, 105 a″ and 107 a″ formed in a secondinsulating layer 103″, a third insulating layer 105″ and a fourthinsulating layer 107″, respectively, each center position of the throughholes alternately changed. The through holes 103 a″, 105 a″ and 107 a″preferably have the same form and the same dimension as each other, oralso preferably have rather different forms and dimensions from eachother. Because the distance between the terminals is short in thethin-film common mode filter, the through holes in the lower layersbecome too small where the through holes in the lower layer to the upperlater are made sequentially larger like the structure in FIG. 10 b.Therefore, it is difficult to improve a reliability in the conductionbetween the layers. Further, because the through holes in the upperlayer to the lower layer have sequentially smaller dimensions, theformed insulating layer has a dimple in the center portion and a narrowthrough hole pattern. Therefore, some residual insulating layer materialor the like causes a high reliable performance of the conduction in thethrough hole to be more difficult. However, by alternately changing theposition of each center of the through holes like the structure in FIG.10 c, the dimple in the through hole becomes smaller, and then thesurface of the insulating layer thereon becomes flatter, and therefore,the surfaces of the through hole conductors and of the insulating layersformed subsequently also become flatter. Consequently, a reliability inthe conduction between the layers is improved, and the step becomessmaller.

Then, the structure of the contact portion as the connection portionbetween the upper coil conductor and the upper lead conductor accordingto the present embodiment will be described.

Smaller capacities between the coil conductors and between the coilconductor and the lead conductor effectively improve high-frequencyproperties of the thin-film common mode filter. However, higher aspectratio, that is height/width, in the coil and lead patterns for theimprovement cause the tolerance of the optimum exposure conditions forforming the contact holes as the connection portions between the uppercoil conductors and the upper lead conductors to be unlimitedly lower.More specifically, an insulating film (photosensitive resin film) isapplied inevitably thickly in the contact hole portion under aninfluence of the adjacent coil during the process. Therefore, an amountof light exposure is needed to increase according to the deepest portionof the film to form the high-precision contact holes. However, under thecondition of an increased amount of light exposure, the light isoverreached to the contact hole portions to be kept unexposed just undermask patterns, by reflections from the adjacent coil or the like, and asthe results, the photosensitive insulating film in the contact holeportion becomes difficult to be dissolved during development. Therefore,a reliability in conduction is reduced. Under the opposite condition ofa decreased amount of light exposure for the purpose of preventing theinfluence of reflections from the adjacent coil, the contact holebecomes larger because of less exposure on the periphery of the contacthole. Further, the decreased amount of light exposure causes a thicknessdecrease of the photosensitive insulating film during development andfails to maintain a pattern accuracy of the insulating film. At worst,the thickness decrease of the insulating film is likely to cause aninsulation failure between the upper coil conductor and the upper leadconductor.

To solve the problems, according to the present embodiment, as shown inFIGS. 8 a and 9, a pedestal part 98 is formed below the contact holebetween the upper coil conductor 16 a or 86 and upper lead conductor 18a or 88, by which the insulating bottom portion underneath the contacthole is lifted up as much as possible. Therefore, because an amount oflight exposure during the contact hole formation is not needed toincrease, the disadvantage such as the lowering reliability inconduction and the insulation failure can be resolved. Particularly,according to present embodiment, because the pedestal part 98 is formedof the conductor layers to be patterned into the lower coil conductor 14a or 84 and the lower lead conductor 12 a or 82, there is no need to adda special process for forming the pedestal part.

As described above, main bodies of the lower lead conductor 12 a or 82,the lower coil conductor 14 a or 84, the upper coil conductor 16 a or86, and the upper lead conductor 18 a or 88 are formed of Cu, and theirexternal surfaces are covered with Ni/Cr films. However, as shown inFIG. 11, the contact portion between the upper coil conductor 16 a or 86and the upper lead conductor 18 a or 88 is covered with only a Cr film.The same is true of the contact portion between the lower lead conductor12 a or 82 and the lower coil conductor 14 a or 84. Thus, a disadvantageof an electric resistance increase caused by the diffusion between Cu/Niis avoided because Ni is eliminated in the contact portion.

Then, a relation between widths of the upper and lower lead conductorsand widths of the upper and lower coil conductors according to thepresent embodiment will be described.

As described above, the higher aspect ratios (height/width) of the coilpattern and of the lead pattern in the thin-film common mode filtercause smaller capacities between the coil conductors and between thecoil conductor and the lead conductor. As the results, thehigh-frequency transmission properties are improved. However, the highaspect ratio design makes it difficult to narrow spacings between thelead conductors and the coil conductors. To solve the difficulty,narrowing widths of the lead conductors is effective.

FIG. 12 shows a characteristic graph illustrating a relation between aresonance frequency of the thin-film common mode filter and the width ofthe lead conductor. The lateral axis of the graph indicates a ratio(W₁/W₂) between the width of the lead conductor (W₁) and the width ofthe coil conductor (W₂), and the longitudinal axis indicates a resonancefrequency.

As understood form the Figure, setting the width of the lead conductor(W₁) not less than twice the width of the coil conductor (W₂) lowers theresonance frequency to a large degree. Therefore, by setting W₁<2W₂, thethin-film common mode filter having an enough high resonance frequency,more specifically, showing no resonance frequency in proximity to 2 GHzused as a communication frequency band can be provided.

Then, a manufacturing process of the thin-film common mode filter arrayaccording to the present embodiment will be described.

FIGS. 13 and 14 show perspective views for explanation of a waferprocess and a working process to produce the thin-film common modefilter array, respectively. In FIGS. 13 a–13 j and FIGS. 14 a–14 d, alower part of the view shows a wafer, and an upper part shows individualchips in the substrate that are not actually cut to separate.

First, as shown in FIG. 13 a, a ferrite wafer 130 is prepared, and, asshown in FIG. 13 b, a first insulating layer 131 made of such as apolyimide resin is coated on the wafer 130, and is then patterned.

Next, as shown in FIG. 13 c, first leads and electrodes made of a copperlayer 132 are formed on the first insulating layer 131. Then, as shownin FIG. 13 d, a second insulating layer 133 made of such as a polyimideresin is coated thereon, and patterned.

Then, as shown in FIG. 13 e, first coils made of a copper layer 134 areformed on the second insulating layer 133. Then, as shown in FIG. 13 f,a third insulating layer 135 made of such as a polyimide resin is coatedthereon, and patterned.

Then, as shown in FIG. 13 g, second coils made of a copper layer 136 areformed on the third insulating layer 135. Then, as shown in FIG. 13 h, afourth insulating layer 137 made of such as a polyimide resin is coatedthereon, and patterned.

Then, as shown in FIG. 13 i, second leads made of a copper layer 138 areformed on the fourth insulating layer 137. Then, as shown in FIGS. 13 jand 14 a, a fifth insulating layer 139 made of such as a polyimide resinis coated thereon, and patterned.

After that, as shown in FIG. 14 b, silver pastes 140 are screen-printedon the lead portions. Then, as shown in FIG. 14 c, ferrite pastes 141for return portions of the magnetic paths are embedded in the coreportions.

Then, as shown in FIG. 14 d, a ferrite plate cover 142 is bonded on theprocessed wafer with an adhesive.

Then, as shown in FIG. 14 e, the obtained wafer is cut into bars 143 oneach of which a plurality of thin-film common mode filter array chipsare aligned.

Then, as shown in FIG. 14 f, a mark 144 is printed on the upper side ofeach of the thin-film common mode filter array chips in the bar 143.Then, as shown in FIG. 14 g, connect electrode terminals 145 made of Niare formed by sputtering on the side of each of the thin film commonmode filter array chips in the bar 133.

After that, as shown in FIG. 14 h, each bar is cut to separate intoindividual chips 146. Then, as shown in FIG. 14 i, the connect electrodeterminals 145 are formed into bilayer structure 147 of a Nickel layerand a tin layer by barrel plating. Further, as shown in FIG. 14 j, theobtained thin-film common mode filter array chips 146 are bonded on atape 148.

All the foregoing embodiments are by way of example of the presentinvention only and not intended to be limiting, and many widelydifferent alternations and modifications of the present invention may beconstructed without departing from the spirit and scope of the presentinvention. Accordingly, the present invention is limited only as definedin the following claims and equivalents thereto.

1. A thin-film common mode filter comprising: a pair of magnetic plates;an upper coil conductor and a lower coil conductor formed between saidpair of magnetic plates, spirally wound in said magnetic plates surfacedirection, and overlapped each other; an upper lead conductor and alower lead conductor, one ends of said upper lead conductor and saidlower lead conductor connected electrically to one ends in centerportions of said upper coil conductor and said lower coil conductor,respectively, and extended to external portions across said upper coilconductor and said lower coil conductor; an upper lead drawing terminaland a lower lead drawing terminal, the other ends of said upper leadconductor and said lower lead conductor connected to said upper leaddrawing terminal and said lower lead drawing terminal, respectively; anupper coil drawing terminal and a lower coil drawing terminal, the otherends of said upper coil conductor and said lower coil conductorconnected to said upper coil drawing terminal and said lower coildrawing terminal, respectively; and each of said lower lead drawingterminal, said lower coil drawing terminal, said upper coil drawingterminal and said upper lead drawing terminal having a structure whereat least two of conductor layers to be patterned into said lower leadconductor, said lower coil conductor, said upper coil conductor and saidupper lead conductor are stacked, and brought into conduction with eachother.
 2. The thin-film common mode filter as claimed in claim 1,wherein each of said lower lead drawing terminal, said lower coildrawing terminal, said upper coil drawing terminal and said upper leaddrawing terminal has a structure where all of said conductor layers tobe patterned into said lower lead conductor, said lower coil conductor,said upper coil conductor and said upper lead conductor are stacked, andbrought into conduction with each other.
 3. The thin-film common modefilter as claimed in claim 2, wherein each of said lower lead drawingterminal, said lower coil drawing terminal, said upper coil drawingterminal and said upper lead drawing terminal has a structure where saidconductor layers to be patterned into said lower lead conductor and saidlower coil conductor are connected to each other via a through hole in afirst layer, said conductor layers to be patterned into said lower coilconductor and said upper coil conductor are connected to each other viaa through hole in a second layer, said conductor layers to be patternedinto said upper coil conductor and said upper lead conductor areconnected to each other via a through hole in a third layer, and all ofsaid conductor layers are brought into conduction with each other. 4.The thin-film common mode filter as claimed in claim 3, wherein centersof said through holes in said first layer to said third layer coincidewith each other.
 5. The thin-film common mode filter as claimed in claim4, wherein said through holes in said first layer to said third layerhave sequentially larger dimensions.
 6. The thin-film common mode filteras claimed in claim 4, wherein said through holes in said first layer tosaid third layer have the same form and the same dimension as eachother.
 7. The thin-film common mode filter as claimed in claim 3,wherein each center position of said through holes in said first layerto said third layer is alternately changed.
 8. The thin-film common modefilter as claimed in claim 7, wherein said through holes in said firstlayer to said third layer have the same form and the same dimension aseach other.
 9. The thin-film common mode filter as claimed in claim 1,wherein widths (W₁) of said upper and lower lead conductors are lessthan twice the widths (W₂) of said upper and lower coil conductors(W₁<2W₂).
 10. The thin-film common mode filter as claimed in claim 1,wherein said lower and upper lead conductors are formed of a copperwhose external surfaces are covered with nickel/chromium films.
 11. Thethin film common mode filter as claimed in claim 10, wherein a surfaceof said lower lead conductor in a connection portion between said lowercoil conductor and said lower lead conductor, and a surface of saidupper lead conductor in a connection portion between said upper coilconductor and said upper lead conductor, are covered with only chromiumfilms.
 12. A thin-film common mode filter array comprising a pluralityof thin-film common mode filters comprising: a pair of magnetic plates;an upper coil conductor and a lower coil conductor formed between saidpair of magnetic plates, spirally wound in said magnetic plates surfacedirection, and overlapped each other; an upper lead conductor and alower lead conductor, one ends of said upper lead conductor and saidlower lead conductor connected electrically to one ends in centerportions of said upper coil conductor and said lower coil conductor,respectively, and extended to external portions across said upper coilconductor and said lower coil conductor; an upper lead drawing terminaland a lower lead drawing terminal, the other ends of said upper leadconductor and said lower lead conductor connected to said upper leaddrawing terminal and said lower lead drawing terminal, respectively; anupper coil drawing terminal and a lower coil drawing terminal, the otherends of said upper coil conductor and said lower coil conductorconnected to said upper coil drawing terminal and said lower coildrawing terminal, respectively; and each of said lower lead drawingterminal, said lower coil drawing terminal, said upper coil drawingterminal and said upper lead drawing terminal having a structure whereat least two of conductor layers to be patterned into said lower leadconductor, said lower coil conductor, said upper coil conductor and saidupper lead conductor are stacked, and brought into conduction with eachother.
 13. The thin-film common mode filter array as claimed in claim12, wherein each of said lower lead drawing terminal, said lower coildrawing terminal, said upper coil drawing terminal and said upper leaddrawing terminal has a structure where all of said conductor layers tobe patterned into said lower lead conductor, said lower coil conductor,said upper coil conductor and said upper lead conductor are stacked, andbrought into conduction with each other.
 14. The thin-film common modefilter array as claimed in claim 13, wherein each of said lower leaddrawing terminal, said lower coil drawing terminal, said upper coildrawing terminal and said upper lead drawing terminal has a structurewhere said conductor layers to be patterned into said lower leadconductor and said lower coil conductor are connected to each other viaa through hole in a first layer, said conductor layers to be patternedinto said lower coil conductor and said upper coil conductor areconnected to each other via a through hole in a second layer, saidconductor layers to be patterned into said upper coil conductor and saidupper lead conductor are connected to each other via a through hole in athird layer, and all of said conductor layers are brought intoconduction with each other.
 15. The thin-film common mode filter arrayas claimed in claim 14, wherein centers of said through holes in saidfirst layer to said third layer coincide with each other.
 16. Thethin-film common mode filter array as claimed in claim 15, wherein saidthrough holes in said first layer to said third layer have sequentiallylarger dimensions.
 17. The thin-film common mode filter array as claimedin claim 15, wherein said through holes in said first layer to saidthird layer have the same form and the same dimension as each other. 18.The thin-film common mode filter array as claimed in claim 14, whereineach center position of said through holes in said first layer to saidthird layer is alternately changed.
 19. The thin-film common mode filterarray as claimed in claim 18, wherein said through holes in said firstlayer to said third layer have the same form and the same dimension aseach other.
 20. The thin-film common mode filter array as claimed inclaim 12, wherein widths (W₁) of said upper and lower lead conductorsare less than twice the widths (W₂) of said upper and lower coilconductors (W₁<2W₂).
 21. The thin-film common mode filter array asclaimed in claim 12, wherein said lower and upper lead conductors areformed of a copper whose external surfaces are covered withnickel/chromium films.
 22. The thin film common mode filter array asclaimed in claim 21, wherein a surface of said lower lead conductor in aconnection portion between said lower coil conductor and said lower leadconductor, and a surface of said upper lead conductor in a connectionportion between said upper coil conductor and said upper lead conductor,are covered with only chromium films.